Converged Internet Protocol Messaging (CPM) denotes a messaging service based upon an Internet Protocol Multimedia Subsystem (IMS), and is a technique for converging and providing several services, such as an existing Short Message Service (SMS), a Multimedia Message Service (MMS), an Instant Messaging (IM) and the like, on the basis of an Internet Protocol (IP).
A CPM session is a type of chatting service for allowing a real-time message communication among users.
Types of messages to be transmitted and received in the CPM session may roughly include a discrete media type and a continuous media type. The discrete media includes audio clip, text, image and the like, and the continuous media includes audio and video. The transmission of the discrete media uses a Message Session Relay Protocol (MSRP), and the transmission of the continuous media uses a Real-time Transport Protocol (RTP).
The MSRP uses a Transmission Control Protocol (TCP) as its sub protocol. The TCP protocol ensures the arrival of packets and keeps the transmission orders among packets, so it is appropriate for an application, such as a messaging service, in which the message transmission should be guaranteed.